In a message dated 6/14/2006 4:47:44 PM Central Standard Time,
75TR6@tr6.danielsonfamily.org writes:
> The Facet fuel pump instructions strongly recommends wiring it to the Oil
> Pressure Switch (OPS) so that it won't pump fuel with the ignition switch on
> unless the engine is running. To quote them "This stops pump operation if
> the engine stops and the ignition switch is on." OK, now my OPS has 3
> terminals (ground, anti-run valve &Oil Pressure Light (OPL)). When I turn
> the key on, the OPL comes on and when the engine starts the OPL turns off.
> So if I hook the pump to that lead, it seems like it would work the opposite
> of what Facet is asking. Turn key on and "pump runs/OPL on" and start car
> "OPL turns off/Pump off"?? So how do I wire this to the OPS? Added to the
> mix is I have Dan's harness with 3 leads from the fuel pump relay: warning
> buzzer, inertia switch &fuel pump.
>
You're assessment is right. If you hook it up to the wire that lights the
light it will run until you get oil pressure and then shut off.
The black wire is ground so you could wire it to that and it will run
whenever the key is on (or you could just connect it to chassis, for that
matter).
The third wire is for the anti-run-on valve. Power for that valve comes from
a special contact on the ignition switch that is hot only when the key is in
the off position. The third contact on the oil pressure switch is closed
(connected to ground) whenever you HAVE oil pressure so when you shut down the
valve will energize until oil pressure falls below the switch setting.
You could wire the pump up to this terminal and get the desired action. In
theory. However, there is a sneak circuit in that the pump and valve will be
wired in series once the switch switches. The pump and valve will pass current
to the rest of the switched loads. They will divide up the 12 volts and they
may continue to operate but even if they don't they will pass current and
drain your battery in short order (overnight).
Worse yet, the voltage across the pump will be reversed. The pump may be
protected against reverse polarity but my advice on reverse polarity protection
on after market fuel pumps is "don't count on it." You could get a DPDT relay
and work up a circuit that will do what you want.
My advice is forget wiring it into the oil pressure switch. If the car sits
with the key on and the engine not running very long you'll burn the points
anyway so not having the pump running for the short amount of time it is likely
to see this situation is not of much benefit. Besides, when the tank is full
you don't even need a pump to get fuel into the carbs so if your float valves
aren't up to snuff you will still have problems.
I wired my pump to the ignition circuit (through a special fuse) through an
impact switch. Any impact switch will do. I got one from a Ford Probe at the
wrecking yard for $5 that was mounted in the boot so it was clean and like
new. This will shut down the pump in the event of a collision where a running
pump may disgorge the contents of the tank into a burning wreck. This is a
consideration worthy of a $5 investment to prevent.
BTW there is usually a Front to these switches so pay attention when you
mount it.
Dave
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